1. Field of the Invention
This invention relates to a photoresist stripping solution and a method for stripping photoresists using the same. More particularly, the invention relates to a photoresist stripping solution which-is excellent, in photolithography, not only in stripping residues such as modified or deteriorated photoresist films occurring after the etching step and the subsequent ashing step and post-etching metal deposition but also in preventing corrosion in the step of stripping and in protecting substrates from corrosion in the step of rinsing with water; and a method for stripping photoresists using the same. The invention is suitable for use in the fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus.
2. Description of Relevant Art
The fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus, comprises the steps of forming a uniform photoresist coating over metallic layers or insulating layers such as an SiO2 film formed on a substrate by CVD; performing selective exposure and development to form a photoresist pattern; selectively etching the substrate having the metallic layers or the insulating layers such as an SiO2 film formed thereon by CVD using the photoresist pattern as a mask to form a microcircuit; and removing the unwanted photoresist layer with a liquid stripper. To remove the unwanted photoresist layer, it has been a practice to use various organic liquid strippers from the viewpoints of safety and stripping capability.
Examples of the metallic layer formed by CVD include those made of aluminum (Al); aluminum alloys (Al alloys) such as aluminum-silicon (Alxe2x80x94Si), aluminum-copper (Alxe2x80x94Cu) and alumi-num-silicon-copper (Alxe2x80x94Sixe2x80x94Cu); titanium (Ti); titanium alloys (Ti alloys) such as titanium nitride (TiN) and titanium-tungsten (TiW); tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN) and copper (Cu). In addition, use may be made of interlevel dielectric layers such as organic SOG (spin-on-glass) layers. These metallic, insulating and interlevel dielectric layers are formed in one or more layers on the substrate.
With the recent tendency toward highly integrated, high-density circuits, dry etching enabling fine etching with a higher density has become the major means. Also, it has been a practice to employ plasma ashing to remove the unnecessary photoresist layers remained after etching. After these etching and ashing treatments, residues comprising modified photoresist films and other components remain as referred to horn-like shaped xe2x80x9cveilxe2x80x9d or xe2x80x9cfencesxe2x80x9d on the bottom or side wall of patterned grooves. In addition, etching of metallic layers builds up metal depositions. Such residues and depositions should be completely removed so as to keep good yields in the production of semiconductors.
In recent years, further high-density integrated substrates are needed and thus the treating conditions in the etching and ashing steps become more and more strict. As a result, metal conductors having much elevated corrosion resistance and stripping solutions showing much improved performance, compared with the conventional ones, are needed. That is to say, none of the conventional stripping solutions is usable in such ultrafine processing.
There have been frequently employed compositions containing fluorine compounds such as hydrofluoric acid in photoresist stripping solutions and liquids for removing modified films remained after ashing. For example, Unexamined Published Japanese Patent Application (Kokai) No. 201794/1995 discloses a cleaner for semiconductor devices containing a specific quaternary ammonium salt, a fluorine compound and an organic solvent; Unexamined Published Japanese Patent Application (Kokai) No. 197681/1997 discloses a resist stripping solution composition containing a salt of hydrofluoric acid with a base free from metal ions and a water-soluble organic solvent and having a pH value of 5 to 8 in the system; Unexamined Published Japanese Patent Application (Kokai) No. 67632/1999 discloses a cleaner for semiconductor devices containing a fluorine compound, a water-soluble organic solvent and water each in a specified amount; and Unexamined Published Japanese Patent Application (Kokai) No. 283507/1997 discloses a stripping agent containing a specific quaternary ammonium hydroxide, a nucleophilic amine compound having redox potential, sugars and/or sugar alcohols and water each at a specified ratio.
However, none of the stripping solutions and cleaners reported in these documents is effective at a practically available level in preventing metal conductors formed on high-density, highly integrated substrates from corrosion.
In addition, stripping solutions and cleaners containing fluorine compounds such as hydrofluoric acid suffer from a problem that substrates frequently corrode away in the step of rinsing with water which is usually performed after stripping and washing.
An object of the present invention, which has been completed under the above-described circumstances, is to provide a photoresist stripping solution which is excellent not only in stripping residues such as metal depositions and modified or deteriorated photoresist films occurring after the step of etching metal layers formed on highly integrated substrates and the subsequent ashing step, but also in corrosion-inhibiting effects in the stripping step and protecting substrates from corrosion in the step of rinsing with water.
Another object of the present invention is to provide a method of stripping photoresists using the above-described photoresist stripping solution.
Thus, according to its first aspect, the present invention provides a photoresist stripping solution which comprises (a) a salt of hydrofluoric acid with a base free from metal ions; (b) a water-soluble organic solvent; (c) a basic substance; and (d) water.
According to its second aspect, the present invention provides a method of stripping photoresists which comprises etching a substrate using a photoresist pattern formed on the substrate as a mask, ashing the photoresist pattern, stripping the ashed photoresist pattern using the photoresist stripping solution as described above, and then rinsing the substrate with water.